1. Field of the Invention
The present invention relates to device and method for controlling ignition timing of an internal combustion engine, and particularly to a technique of controlling ignition timing based on whether knocking is present or absent.
2. Description of the Background Art
Conventionally, various methods of determining whether knocking (knock) is present or absent have been proposed. For example, by detecting magnitude of vibration occurring in an internal combustion engine and comparing the magnitude with a threshold value, whether knocking is present or absent is determined. However, in an internal combustion engine, besides vibration due to knocking, vibration due to an intake valve or an exhaust valve sitting on its seat may occur. Vibration may also occur due to the actuation of an injector (in particular, an in-cylinder direct injector that directly injects fuel inside a cylinder) or a high-pressure pump that supplies fuel to the injector. When such vibration is detected as noise, it may not be possible to discriminate vibration due to knocking from vibration due to noise, based on magnitude of vibration. Accordingly, a technique of determining whether knocking is present or absent in consideration of both magnitude of vibration and a waveform shape has been proposed.
A knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2003-021032 includes: a knock sensor detecting knocking in an internal combustion engine; a statistical processing portion statistically processing an output signal detected by the knock sensor; a first temporal determination portion determining occurrence of knocking based on a processing result by the statistical processing portion; a second temporal determination portion determining occurrence of knocking based on a waveform shape of the output signal detected by the knock sensor; and a final knock determination portion finally determining occurrence of knocking based on the knock temporal determination of the first temporal determination portion and the knock temporal determination of the second temporal determination portion. When both of the first and second temporal determination portions determine that knocking has occurred, the final knock determination portion finally determines that knocking has occurred. In the first temporal determination portion, by comparing the maximum value of the output signals detected by the knock sensor with a knock determination level calculated based on the processing result by the statistical processing portion, whether or not knocking has occurred is determined. A knock determination level is corrected to a value obtained by subtracting a set value ΔV from the knock determination level or to a value obtained by adding the product of a value A greater than “1” and set value ΔV to the knock determination level, based on the occurrence frequency of knocking. In a distribution of values LOG(V), which are obtained by logarithmically converting maximum values V of knock sensor output signals, it is assumed that the highest 10% values, the highest 50% values, and the highest 90% values are V10, V50, and V90, respectively. When knocking frequently occurs, they are in the relationship of V10/V50>V50/V90. Accordingly, when V10/V50>V50/V90, set value ΔV is subtracted from the knock determination level to correct the knock determination level. When V10/V50>V50/V90 is not satisfied, the product of “A” and set value ΔV is added to the knock determination level to correct the knock determination level.
According to the knock control device disclosed by the publication, a knock temporal determination by a statistical processing program and a knock temporal determination by a waveform shape program are used, and only when both of the temporal determinations determine that knocking has occurred, it is finally determined that knocking has occurred. As a result, occurrence of knocking can precisely be determined even as to an output signal, which has been erroneously determined by a knock determination employing solely the statistical processing program or the waveform shape program.
However, even when whether knocking is present or absent is determined using the distribution of magnitudes (output signals of the knock sensor) of vibration occurring in the internal combustion engine as in the knock control device described in Japanese Patent Laying-Open No. 2003-021032, not always a determination value (knock determination level) is precisely corrected. When knocking occurs extremely frequently, both the highest 10% values and the highest 50% values can be great. Therefore, sometimes V10/V50>V50/V90 is not satisfied even though knocking frequently occurs. In such a case, even though knocking has occurred, the determination value (knock determination level) may be increased. Therefore, even though knocking has occurred, it may hardly be determined that knocking has occurred. Accordingly, ignition timing may be advanced and the occurrence of knocking cannot be suppressed.